This invention relates to schemes for improving lubricant flow, and in particular, the return of lubricant from various locations in a refrigerant cycle back to a compressor, to prevent an inadequate supply of lubricant to the compressor.
Refrigerant cycles typically include a compressor for compressing a refrigerant and delivering that refrigerant downstream to a condenser. From the condenser the refrigerant passes to an expansion device that expands the refrigerant. From the expansion device, refrigerant moves to an evaporator. The evaporator is a heat exchanger that typically changes the temperature in an environment to be conditioned. From the evaporator, the refrigerant may run through a modulation valve before returning to the compressor. The evaporator often captures refrigerant and lubricant as it has traveled through the refrigerant cycle. Lubricant is typically necessary in the compressor to lubricate the moving parts. However, as the lubricant is delivered to the compressor, it is often entrained in and with the refrigerant, and travels through the refrigerant cycle. While the evaporator is specifically mentioned, oil can accumulate in other locations, and the present invention assists in returning oil from these other locations.
The conditions in the evaporator often result in lubricant leaving the refrigerant, and remaining trapped in the evaporator. At some point, there may be an inadequate supply of lubricant in the compressor, which is undesirable. Oil retention in the evaporator can also adversely affect the heat transfer within the evaporator, reducing efficiency and capacity of the unit, which is also undesirable.